This invention is generally directed to processes for the preparation of a polymer or polymers, and toner compositions thereof, and more specifically to bulk and semisuspension polymerization processes. In one specific embodiment, the present invention is directed to economical and noncomplex processes for the preparation of polymers containing both a water soluble, and an oil soluble component. Also, in embodiments the present invention relates to processes for obtaining polymers containing two or more monomers, at least one of which is water soluble, and at least one of which is oil soluble by the combination of bulk polymerization, and suspension polymerization. The polymer or polymers resulting can be selected as toner resins for toner compositions, reference U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, as carrier coatings, toner additives, and the like. In embodiments, the polymer particles obtained with the processes of the present invention can possess an average particle diameter of from between about submicron, for example 0.1 micron to about 350 microns, and preferably from between about 1 to about 20 microns.
Copolymers and terpolymers containing at least one water soluble component, and one oil soluble component cannot be effectively obtained by known heterogeneous polymerizations because, for example, of the solubility of the hydrophilic component in the continuous phase. Water-soluble monomer refers in embodiments to monomers having greater than about 10 weight percent solubility in water and oil-soluble monomer refers in embodiments to those monomers having less than about 10 weight percent solubility in water. Consequently, such polymers are usually prepared by solution polymerizations, which are economically less attractive than heterogeneous processes in view of, for example, the lower polymerization rates, inferior heat transfer, and increased costs because of the use of a solvent and its removal. It is desirable to incorporate water soluble monomers into a polymer product to, for example, increase the range of its electrical and physical properties, for example, to effect the modification of the triboelectric characteristics of the polymer, and control the tribo properties of toner compositions thereof.
Semisuspension polymerization processes for the preparation of polymers are illustrated in U.S. Pat. No. 5,043,404, the disclosure of which is totally incorporated herein by reference. Also, U.S. Pat. No. 3,954,898 relates generally to specific bulk and suspension polymerizations, see the Abstract for example; and 4,592,990 relates to toner processes, see column 8 for example.
Disclosed in copending patent application U.S. Ser. No. 339,539 (D/88092), the disclosure of which is totally incorporated herein by reference, are semisuspension polymerization processes for the economical preparation of toners with, for example, an average diameter of from about 5 to about 25 microns, wherein a mixture of monomer or comonomers, a polymerization initiator, a crosslinking component and a chain transfer component are bulk polymerized until partial polymerization is accomplished, for example from about 10 to about 40 percent of monomer or comonomers is converted to a polymer, followed by adding to the formed partially polymerized polymer pigments, or dyes optional additives such as charge control materials, low molecular weight waxes such as polypropylene, or polyethylene, and the like, and mixing with, for example, a high shear mixer to obtain a homogeneous organic mixture, subsequently dispersing the resulting organic mixture in water containing a stabilizing component, which dispersing can be accomplished, for example, by a high shear mixer, transferring the resulting suspension to a reactor, and effecting polymerization thereof, followed by optional washing, and drying. The toner composition obtained can be optionally blended with surface additives, which may function as flow aids, such as colloidal silicas and the like.
As a result of a patentability search in the aforementioned copending patent application there were located U.S. Pat. No. 4,486,559, which discloses the incorporation of a prepolymer into a monomer toner mix followed by emulsion polymerization; U.S. Pat. Nos. 4,680,200 and 4,702,988, which illustrate emulsion polymerization. Also, U.S. Pat. No. 2,886,553 relates to polymerization processes.
Toners can generally be prepared by fusion mixing of pigments (colorants), charge control agents and other additives into thermoplastic resins to disperse them uniformly therein. In view of the high viscosity of the aforementioned mixture, a considerable amount of energy is usually needed to achieve a uniform dispersion of pigments and other additives in the toner resin. The mixture is then cooled, followed by pulverization and classification into desired particles sizes and particle size distribution. It is known that pulverization is an energy intensive step in this process. This preparation method is capable of producing excellent toners, however, it requires the use of a several steps which can be costly, energy intensive and limited in certain respects. In the process for generating toners by pulverization, the material being pulverized must usually be fragile to permit it to be readily pulverized. Therefore, some thermoplastic resins which are not fragile but have acceptable fusing performance may not be selected for the aforementioned prior art processes. Also, if the material being pulverized is too fragile, it may be excessively micropulverized and, therefore, the fines portion of the particles must usually be uneconomically removed. These limitations become increasingly severe for smaller particle size toners, that is with for example a volume average particle size of from about 3 to about 9 microns. Also, when a material such as a polymer resin with a low melting point is employed to improve fusing performance of the toner, the fusion of such material may occur in the pulverizing device or the classifier.
Attempts to prepare copolymers or terpolymers containing a significant portion of water-soluble monomer by traditional suspension polymerizations are prone to failure because the water-soluble components will rapidly diffuse into the aqueous phase, leaving only the oil-soluble monomers in the polymerizing particles. The water-soluble monomers will then solution polymerize in the aqueous phase if a source of free radicals is available. However, if the initial viscosity of the suspended droplets is sufficiently high, and for example if the conversion is between approximately 10 to 40 percent depending on the molecular weight, which varies from about 10,000 to 200,000, the diffusion rate of the water-soluble components will be severely hindered. As a result, these monomers will polymerize in the droplets before they have an opportunity to diffuse into the aqueous phase. The higher the initial viscosity the more restricted is the monomer diffusion; however if the initial viscosity is too high it will not be possible to effectively form small particles with a narrow particle size distribution.
Accordingly, to remove or minimize the disadvantage of the pulverization method, there have been proposed processes for producing toner wherein the toner particles were formed and the desired particle size distribution produced in a reactor. These processes include dispersion polymerization, suspension polymerization, emulsion polymerization, and the like. Disclosed in U.S. Pat. No. 4,486,559 is the preparation of a toner composition by the incorporation of a prepolymer into a monomer/pigment mixture, followed by emulsion polymerization, see for example columns 4, 5 and 8 of this patent. Also, methods of preparing toner, including suspension/dispersion polymerization, are illustrated in columns 1 and 2 of this patent. In these processes, the pigment and additives such as charge control components are added to a monomer, or comonomers prior to polymerization. Particle formation is achieved by the dispersion of the pigmented monomer or comonomers in a continuous phase such as water, and the droplets of pigmented monomers are then polymerized to form toner particles. One advantage of these processes as compared to other methods is the elimination of fusion mixing (Banbury/extruder) and pulverization classification processing. Nevertheless, it can be difficult with these processes to accomplish polymerization of pigmented monomer droplets in a diameter range of 5 to 25 microns with a narrow distribution of, for example, 1.3. Also, suspension failure is common with these processes especially when the monomer droplet diameter is less than 50 microns and as polymerization proceeds in the sticky region (10 to 40 percent conversion). Further, it is difficult to conduct the polymerization of pigmented monomer droplets since, for example, it is known that polymerization of free radical type monomers are hindered, and may be prevented by the presence of various pigments, especially carbon black. Another disadvantage of these processes for the preparation of toners resides in the resulting poor dispersion of the pigment and other additives within the toner particles which is believed to be caused by the lack of micromixing, that is the diffusional mixing within the monomer droplet. Moreover, many of the prior art processes for the preparation of polymer particles is costly, or not as economical as desired. These and other disadvantages are avoided or minimized with the bulk, and semisuspension polymerization processes of the present invention.